American Journal of Botany 92(9): 1548±1558. 2005. MOLECULAR PHYLOGENY OF ORYZEAE (POACEAE) BASED ON DNA SEQUENCES FROM CHLOROPLAST, MITOCHONDRIAL, AND NUCLEAR GENOMES1 YA-LONG GUO2 AND SONG GE2,3,4 2Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; and 3Graduate School, Chinese Academy of Sciences, Beijing 100039, China The phylogeny and evolutionary history of the rice tribe (Oryzeae) were explored using sequences of ®ve DNA fragments (matK, trnL, nad1, Adh2, and GPA1) from chloroplast, mitochondrial, and nuclear genomes. Results indicate that (1) Oryzeae is monophyletic and falls into two main clades corresponding to the traditionally recognized subtribes; (2) previous recognition of three monotypic genera (Hydrochloa, Porteresia, and Prosphytochloa) is not justi®ed; and (3) close af®nities of the monoecious genera are not sup- ported, suggesting the possibility of multiple origins of unisexual ¯orets. Based on the magnitude of matK and GPA1 sequence divergence, we suggest that Oryza and Leersia branched off from the remaining genera of Oryzeae ;20 million years ago (mya), and separated from each other ;14 mya. A divergence time of ;9 mya is obtained for the most basal split within Oryza. These estimates suggest that Oryzeae diverged during the Miocene, and thus imply that long-distance dispersal appears to be one of the important factors in the diversi®cation of the tribe. Key words: biogeography; divergence time; multiple sequences; Oryzeae; phylogeny. The tribe Oryzeae (Poaceae), as conventionally delimited, cies of Oryza that contain agronomically useful traits for rice includes approximately 12 genera and more than 70 species genetic improvement, Zizania species that are a well-known distributed throughout the tropical and temperate regions of part of cuisine in China (Z. latifolia) and North America (Z. the world (Clayton and Renvoize, 1986; Vaughan, 1994). As palustris L.), and Leersia species that are useful forage the largest tribe in the subfamily Ehrhartoideae, Oryzeae con- (Vaughan, 1994; Kennard et al., 1999). Importantly, rice is tains more than half of both genera and species of the subfam- becoming an excellent research model due to its small genome ily (Watson and Dallwitz, 1999; GPWG, 2001). In this tribe, size, ef®cient genetic transformation, and extensive colinearity Oryza L. with approximately 23 species and Leersia Sw. with with other grass species (Gale and Devos, 1998; Schmidt, approximately 18 species are the two largest genera and dis- 2000; Shimamoto and Kyozuka, 2002). In particular, the com- tributed worldwide (Watson and Dallwitz, 1999; Terrell et al., pletion of the rice genome sequence provides tremendous val- 2001). Except for Zizania L., which is disjunctly distributed ue of rice as a model plant (Bennetzen, 2002; Rensink and in eastern Asia and eastern North America, the remaining nine Buell, 2004). Therefore, a clear picture of phylogenetic rela- genera are distributed regionally or con®ned to a speci®c con- tionships of rice and its relatives will provide an important tinent (Watson and Dallwitz, 1999). Chikusichloa Koidz and foundation for future breeding programs and for biological two monotypic genera (Hygroryza Nees and Porteresia Tateo- studies of rice and grasses in general (Kellogg, 1998; Ge et ka) are distributed in Asia. Zizaniopsis Doell ex Asch. and al., 2001; Rensink and Buell, 2004). Luziola Juss., as well as the monotypic Rhynchoryza Baill., Because of the economical and theoretical importance of occur in North and South America, while monotypic Pota- rice, classi®cation and phylogeny of Oryza and its closely re- mophila R. Br. is endemic to Australia and Prosphytochloa lated genera have been studied through various approaches Schweick. to Africa. including morphology (Weatherwax, 1929; Launert, 1965; In the genus Oryza, the Asian cultivated rice (O. sativa)is Terrell and Robinson, 1974; Kellogg and Watson, 1993; Terrell one of the world's most important crops and a primary food et al., 2001), cytology (Ramanujam, 1938; Li et al., 1963; source for more than one-half of the world's population (Chan- Nayar, 1973), restriction site analysis (Zhang and Second, dler and Wessler, 2001; Ge et al., 2001). Other members of 1989; Duvall et al., 1993), and DNA sequencing (Ge et al., Oryzeae have important economic value, such as the wild spe- 2002; Hass et al., 2003). Although evidence showed that this 1 Manuscript received 27 December 2004; revision accepted 16 May 2005. tribe was a distinct and monophyletic group (Duistermaat, The authors thank Bao-Rong Lu, Jun Wen, Bruce G. Baldwin, Curtis A. 1987; Zhang and Second, 1989; Kellogg and Watson, 1993; Jones, and Jian-Hua Li for help in collecting materials; Zhen-Yu Li and Fu- Ge et al., 2002), its subdivision and phylogenetic relationships Wu Xing for identifying the samples; and Shou-Zhou Zhang, Fu-Min Zhang, among genera have been inconsistent among studies (Hitch- Ying Bao, Qi-Hui Zhu, Fu-Hong An, and Yang Yu for technical assistance. cock, 1920; Hubbard, 1934, 1959; Hitchcock and Chase, 1951; We also thank De-Yuan Hong, Tao Sang, and Bao-Rong Lu for their encour- agement and support. Comments and suggestions from Paul M. Peterson and Stebbins and Crampton, 1961; Pyrah, 1969; Terrell and Rob- an anonymous reviewer are sincerely appreciated. We are grateful to the In- inson, 1974; Duvall et al., 1993). Previous morphological in- ternational Rice Research Institute (Manila, Philippines) for providing most vestigations treated the oryzoid grasses as a taxonomic bifur- seed and leaf samples used in this study. This study was supported by grants cation of monoecious vs. bisexual groups and recognized the from the Program for Key International Science and Technique Cooperation two groups variously at tribal (Oryzeae vs. Zizanieae) (Hitch- Project of P. R. China (2001CB711103), the National Natural Science Foun- dation of China (30025005, 30121003), and the Chinese Academy of Sciences cock, 1920; Hitchcock and Chase, 1951; Stebbins and Cramp- (kscxz-sw-101A). ton, 1961) or subtribal (Oryzinae vs. Zizaniinae) (Hubbard, 4 Author for correspondence (e-mail: [email protected]) 1934, 1959; Pyrah, 1969) levels. Through morphological and 1548 September 2005] GUO AND GEÐPHYLOGENY OF ORYZEAE BASED ON MULTIPLE DNA SEQUENCES 1549 anatomical investigations, Terrell and Robinson (1974) estab- seven genera, including ®ve monotypic genera (Hygroryza, Porteresia, Po- lished a new subtribe Luziolinae and proposed a three-subtribe tamophila, Prosphytochloa, Rhynchoryza), were sampled. Based on a recent system, but this treatment was not supported by later studies comprehensive study of the subfamilial classi®cation of the grass family of restriction sites and sequence data (Zhang and Second, (GPWG, 2001), the subfamily Ehrhartoideae includes three tribes: Ehrharteae, 1989; Duvall et al., 1993; Ge et al., 2002). In addition, the Oryzeae, and Phyllorachideae, and the tribe Ehrharteae is the most closely delimitation and taxonomic position of some genera in this related tribe to Oryzeae. Therefore, we chose one species of the genus Ehr- tribe have long been problematic and are still controversial harta Thunb. as an outgroup. One additional species of the closely related mainly due to limited samples or insuf®cient character infor- subfamily Bambusoideae was also included in the phylogenetic analysis as mation used in previous studies. For example, the mutually an outgroup. The details of the sampled species with their scienti®c names, exclusive hypotheses that Zizania is more closely related to accession numbers or vouchers, origins, chromosome numbers, and GenBank the monocious genera or to the bisexual genera have been in accession numbers are listed in the Appendix. Total DNA was isolated from silica-gel dried or fresh leaves using the cetyltrimethylammonium bromide dispute for decades (Terrell and Robinson, 1974; Duvall et al., (CTAB) method as described previous by Ge et al. (1999). 1993; Ge et al., 2002). Whether or not to place the monotypic genus Hydrochloa Beauv. in synonymy under Luziola and to Ampli®cation, cloning, and sequencingÐTo amplify the chloroplast matK treat the monotypic genus Porteresia as a member of Oryza and trnL intron, mitochondrial nad1 intron 2, and nuclear Adh2 and GPA1, are also not resolved with certainty (Terrell and Robinson, the polymerase chain reactions (PCR) were carried out in a volume of 25 mL, 1974; Duvall et al., 1993). containing 5±50 ng of genomic DNA, 5.0 pmol of each primer, 0.2 mM of Based on sequences of the chloroplast matK gene, Ge et al. each dNTP, 2 mM MgCl2 and 0.65 units of Taq DNA polymerase. Ampli®- (2002) studied the phylogeny of Oryzeae. They veri®ed that cations were performed in a Peltier thermal cycler (PTC-200, PerkinElmer the tribe was a monophyletic group consisting of two strongly Corporation, Wellesley, USA) . supported monophyletic groups corresponding to the two tra- The primers for amplifying and sequencing matK followed those in Ge et ditionally recognized subtribes, and they also suggested treat- al. (1999). Most sequences of matK were used in Ge et al. (2002), but ad- ing Porteresia as a member of Oryza. Although the matK work ditional sequences from Leersia oryzoides, Luziola ¯uitans, and Ehrharta er- was so far the most comprehensive phylogenetic study of this ecta were generated in this study. The chloroplast trnL intron was ampli®ed tribe using sequence data in terms of species and generic in- and sequenced with primers trn-L1 and trn-L2. The two primers, located on clusion, many of the questions just mentioned remain unsolved the 59 exon and 3 exon of the trnL gene, respectively, were designed based or the answers uncertain because of the relatively low reso- on sequences of Oryza sativa (GenBank accession X15901), Triticum aesti- lution of the chloroplast gene. Growing examples in the recent vum L. (AF148757), and Zea mays L. (X86563). The entire intron of mito- literature have demonstrated that low-copy nuclear genes have chondrial nad1 intron 2 and a small part of the 39 exon was ampli®ed and great potential to compensate cpDNA and nrDNA for im- sequenced using the primers of Demesure et al.
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